package com.wjw.leetcode;

import com.wjw.common.ListNode;

/**
 * merge-two-sorted-lists
 * 合并两个有序链表
 */
public class leetcode21 {

    // 迭代
    public ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
        ListNode pre = new ListNode(0);
        ListNode curr = pre;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                curr.next = l1;
                l1 = l1.next;
            } else {
                curr.next = l2;
                l2 = l2.next;
            }
            curr = curr.next;
        }

        if (l1 != null) {
            curr.next = l1;
        }
        if (l2 != null) {
            curr.next = l2;
        }
        return pre.next;
    }

    // 递归
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) return l2;
        if (l2 == null) return l1;
        if (l1.val < l2.val) {
            l1.next = mergeTwoLists(l1.next, l2);
        } else {
            l2.next = mergeTwoLists(l1, l2.next);
        }
        return l1.val < l2.val ? l1 : l2;
    }
}
